Multiple Myeloma (MM) is the prototype of a clonal B-cell malignancy. Hematopoietic stem cell (HSC) transplantation and/or novel chemotherapy combinations have improved long-term disease free survival. However, relapse of the underlying disease remains the primary cause of treatment failure with MM being essentially an incurable disease. Therefore, strategies aiming to improve treatment efficacy are much needed. The central hypothesis of this project is that bone marrow sub-populations in MM patients constitute a progenitor compartment with self renewal capacity that is responsible for disease initiation, maintenance and progression. These cells may have a specific signature to render them insensitive to chemotherapy and they may rely on the hematopoietic stroma microenvironment for their survival. Our preliminary results show that MM patient's bone marrow contain a clonal sub-population that do not express syndecan-1 (CD138-), differentiates in clonogenic assay to a mature cell (CD138+) and is relatively resistant to bortezomib treatment. The proposed study will contribute to the understanding of MM biology analyzing the phenotypic and unique make up of a MM progenitor sub-population that may be in part responsible for disease initiation and/or relapse. Our future goal is to establish the clinical significance of these cells and to develop drugs and/or immune therapies to target all MM sub-populations. In Aim 1, we will determine the differentiation potential and self-renewal capacity of CD138- MM cells. We proposed to characterize phenotypic differentiation of CD138- MM cells and establish their chromosomal signature. We plan to define their clonality with patient-specific immunoglobulin heavy chain rearrangements and clonogenicity in vivo. In Aim 2, we will determine the role of self renewal pathways as an intrinsic mechanism of resistance of CD138- MM sub-populations by analyzing related proteins by mass spectrometry. We will test the effect of self renewal ligands on protein expression, on cell proliferation, on activation of target genes and clonogenic growth of CD138- cells. In Aim 3, we will determine the role of stroma cells in conferring a survival advantage to CD138-cells. I hypothesize that the microenvironment supports CD138- MM cells clonogenicity and these cells depend on it signals for their survival as the stroma provides a supporting niche. I postulate that stroma elements may provide cyto-protection to CD138- MM subpopulations in part due to perturbations in cell cycle progression and/or known MM-stroma survival mechanism. In pursuit of this aim we will assess stroma related cytokines and fibronectin effect on cell cycle and on modulation of protein expression of BcL-2 apoptotic regulators by mass spectrometry and correlation with drug response. PUBLIC HEALTH RELEVANCE: Multiple Myeloma (MM) is an incurable hematological malignancy of plasma cells. Plasma cells grow in the bone marrow (BM) and produce same type of abnormal antibodies (clone). Development of strategies to improve treatment efficacy and to prevent recurrence of disease (relapse) are much needed. An important cause of treatment failure in cancer is drug resistance leading to minimal residual disease (MRD). Developing novel treatment strategies to target mediators of MRD is essential for complete disease eradication. The "cancer stem cell" concept debates that some cells within the tumor are the root of cancer by producing cancer cells and cancer cure depends on the eradication of these cells. To date, the clinical role of these cells is cancer biology is unknown and deep understanding of these cells in MM remains to be determined. Our preliminary results show that MM BM contains a clone of cells that do not express markers used to identify mature MM cells (plasma cells) and are less susceptible to chemotherapy. We hypothesize that these cells maybe responsible for the origin of MM and responsible for MRD. We propose to establish whether these cells play a role in MM generation and to understand growth regulation mechanisms of these cells. We plan to study self renewal pathways and interaction with the BM micro-environment since we believe that this niche provides positive feedback for their survival. Understanding the role of these cell in MM and decipher their survival tools will be essential since eradication of these cells should produce curative results in MM if hypothesis is proven.